CA1197608A - Device for correcting colour information supplied by a television camera with a view to improving the perception of pictures - Google Patents
Device for correcting colour information supplied by a television camera with a view to improving the perception of picturesInfo
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- CA1197608A CA1197608A CA000403228A CA403228A CA1197608A CA 1197608 A CA1197608 A CA 1197608A CA 000403228 A CA000403228 A CA 000403228A CA 403228 A CA403228 A CA 403228A CA 1197608 A CA1197608 A CA 1197608A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N9/00—Details of colour television systems
- H04N9/77—Circuits for processing the brightness signal and the chrominance signal relative to each other, e.g. adjusting the phase of the brightness signal relative to the colour signal, correcting differential gain or differential phase
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
- H04N23/10—Cameras or camera modules comprising electronic image sensors; Control thereof for generating image signals from different wavelengths
- H04N23/13—Cameras or camera modules comprising electronic image sensors; Control thereof for generating image signals from different wavelengths with multiple sensors
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- Engineering & Computer Science (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
- Processing Of Color Television Signals (AREA)
- Color Television Image Signal Generators (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The correction consists in correcting the overall luminance, whilst retaining the original chromaticity of the analysed picture. For this purpose, the device according to the invention comprises a correcting circuit receiving the colour signals Ve1, Ve2 and Ve3 and supplying corrected colour signals, a matrixing circuit supplying the overall luminance signal Ve, and a control circuit calculating eight transfer parameters defining the transfer function F, which transforms the signal Ve into a signal F(Ve) covering the scale of luminances in accordance with an equal distribution in order to satisfy the optimum vision conditions. The control circuit processes the signal and the correcting circuit supplies corrected colour signals respectively corresponding to the products Ve1 ? , Ve2 ? and Ve3 ?
The correction consists in correcting the overall luminance, whilst retaining the original chromaticity of the analysed picture. For this purpose, the device according to the invention comprises a correcting circuit receiving the colour signals Ve1, Ve2 and Ve3 and supplying corrected colour signals, a matrixing circuit supplying the overall luminance signal Ve, and a control circuit calculating eight transfer parameters defining the transfer function F, which transforms the signal Ve into a signal F(Ve) covering the scale of luminances in accordance with an equal distribution in order to satisfy the optimum vision conditions. The control circuit processes the signal and the correcting circuit supplies corrected colour signals respectively corresponding to the products Ve1 ? , Ve2 ? and Ve3 ?
Description
lo V8 BACKGROUND OF THE INVENTION.
The present invention relates to devîces or correcting colour inforrnation supplied by a camera of a video transmission system with a view to obtaining, on reception, a picture containing the maximum of visible information.
In black and white picture transmission systems-, a correction device for improving the per eption of ( pictures is already known (u.5. Patent Jo. k 337 514 granted to Applicant on June 29, 19~2.) The process performed by this device consists of correcting the luminance signal supplied by the camera or pickup tube of a black and white camera by means of a non-linear quadripole with variable characteristics and controlled L5 in such a wry that the histogram of the values of the corrected luminance signal his a flat form whatever the shooting conditions, which corresponds to a regular 1 distribution of the values on the scale of said values.
- In its present form, this correction device does not make it possible to improve colour pictures, it only being usable in connection with the irnprovement of the black and white pictures.
BRIEF SUMMARY OF THE INVENTION
The present invention relates to a correction device, which makes it possible to improve the perception of colour pictures. The problem consists in correcting the overall luminance in accordance with the method used ' '' 3~''' by the known device, whilst retaining the origi.nal chromaticity of the analysed picture.
The present invention specifically relates to a device for correcting colour information signals of values V l Ve2 and Ve3 supplied by a television camera, comprising a determination circuit having three inputs respectively receiving the three colour informationsignals and an output, for supplying a signal of value V which is`
a function of the values of the colour information signals ;a control circuit having an input coupled to the output of the determination circuit and having an output for F(Ve) supplying a signal of value G(Ve) = V --- , in which F is a function such that the histogram of values F(Ve) us a function of the values Ve has,a predetermined distribution chosen for improving the perception of images ; and a correction circuit having three first inputs respectively receiving the three colour information signals, a second input coupled to the output of the control circuit and having three outputs constituting the outputs of the device according to the invention,'for supplying three signals which are functions of the value G(Ve) and of the values Vel, Ve2, Ve3 respectively-BRIEF DESCRIPTION OF THE DRAWINGS
The invention is described in greater detail hereinafter relative to non-limitative embodiments and the attached drawings, wherein show:
Fig 1 a first embodiment of the device according to the invention.
'Fig 2 a second embodiment ox the device according to the invention.
. . .
Y
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the first embodiment, the device according to the invention receives three colour information signals of valuec V l V 2 and Ve3 , respectively constituted by three blue green and red signals of values EB, EV and ER respectively applied to the three inputs terminals 1, 2 and 3. At the output terminals 15, 16 and 17 it supplies three corrected colour informa-tion signals of values Vsl, Vs2 and Vs3~ The overall luminance value is.
Ey = 0.11~EB 0.59~EV 0.3DER
= O.ll.V 1 0.59.Ve2 .3Ve3 The correction of the overall luminance consists multiplying this value by a variable coefficient G:
Ey corrected = Ey . G
As the value Ey is a linear combination of Ev, ER
and EB for retaining the chromaticity it is merely necessary to multiply the three values Ev, ER and EB by the same coefficient G. Coefficient G varies when Ey varies, because it is determined in such a way as to flatten the histogram of values Ve of a signal constituted, in this embodiment9 by the overall luminance signal. The correction device according to the invention supplies in this case three colour signals having as the corrected value:
Vsl = G(Ve)~Vel with V = En Vs2 = G(Ve)'Ve2 Vel B
VS3 = G(Ve)~Ve3 V = E
V 3 = ER
Fig 1 is a block diagram of the first embodiment ox the device according to the invention utilizing this --3~
, .
go process. Fig 1 shows the three input terminals 1, 2 and 3 for respectively receiving the three colour signals Vel, Ve2 and Ve3 supplied by the pickup tubes of a colour camera. These three inputs are respectively coupled to the three inputs of a circuit 4 for the determination of a signal Ve, constituted by a matrixing circuit 4. The output of matrixing circuit 4 supplies signal Ve which, in this embodiment9 comprises the overall luminance signal. This signal is deduced from the colour signals Vel, Ve2 and Ve3 in accordance with the following formula:
V 0 11 V + o.59jVe2 3'Ve3~(Vel' e2 e3 corresponding respectively to the blue, green and red colour signals).
The output of matrixing circuit 4 is connected to one input of a control circuit 6. Control circuit 6 comprises the acquisition means 14 of a histogram, an analog quadripole 11 and an analog divider 13, each having an input connected to the input of control eireuit 6 , whilst it also eomprises ealeulation means 13 and auxiliary calculation means 12. Quadripole 11 is non-linear and has variable characteristics regulatable by e-ight control inputs el to e for receiving eight signals defining the transfer parameters of the quadripole. Quadripole 11 is of the known type having a broken line transfer function constituted by a predetermined number of linear segments. In the present embodiment, quadripole 11 has been chosen with eight variable transfer parameters and specifically four pairs, constituted by ~976~
a threshold value and a gain value defining four segments. Such a quadripole comprises four, not shown amplifiers having a regula-table t`hreshold below which each signal is not transmitted and above which the signals are transmitted with a fixed gain. Thus, quadripole 11 supplies a corrected luminance signal F(V ), F being the transfer function of the quadripole.
This signal F(Ve), corresponds to the sum of the four output signals of the four amplifiers of the quadripole and is supplied to a second input of the divider 10 and to a second output of control circuit 6.
Means 14 statis-tically analyse the amplitude distribution of 4000 samples of luminance signals Ve in accordance with 64 given amplitude levels. The 4000 samples result from the analysis of 4000 ranges all covering a frame, and the 64 amplitude levels are distributed at regular intervals over the entire scale of the amplitudes of the luminance. Thus, means 14 make it possible to acquire the function representative of the histogram of the luminance (number of samples for each of the envisaged 64 levels).
The calculation means 13, whose input is connected to the output of means 14, calculated the integral of this function which, by definition, is the cumulative distribution function of the amplitude levels of the samples.
On the basis of this cumulative distribution function, the auxiliary calculating means 12, having an input connected to the output of means 13 and 8 outputs respectively connected to the 8 control inputs el to e8 of the quadripole 11, calculate the values of the 8 transfer parameters Al to A4 and Gl to G4 to be applied to the control inputs el to e$, Ai and Gi (i varying from 1 to 4) respectively representing 5 the threshold values and the gain values of the amplifiers of the quadripo~e, The calculated values are such that the transfer function F realised by quadripole 11 is an approximation by segments of the cumulative distribution function calculated by means 13.
10 The values of the thus determined parameters remain fixed throughout the duration of the following frame.
f Such a transfer function transforms the luminance signal Ve into a corrected signal F(Ve) for which the distribution of the values permits a better 15 vision9 no matter what the shooting conditions.(ln the present embodiment 7 the distribution corresponds to an equalization of the luminance histogram associated with the signal F(V ) ).
The assembly constituted by quadripole 11, the 20 histogram acquisition means 14, the calculating means 13 and the auxiliary calculating means 12 exactly corresponds to the automatic control device described in detail in the aforementioned U.S.Patent no. 4337514 The control circuit 6 also comprises the analog divider 25 10 having two inputs respectively receiving the signals of value Ve and F(Ve) and having an output, constituting the first output of the control circuit, and supplying a signal of value G(Ve) = (Ve) ~t~6~38 The object of the invention is to correct the colour information Vel, Ve2 and Ve3 in order that the overall luminance information, associated with the corrected colour informations, corresponds to the luminance inormation contained in signal F(Ve), whilst retaining the original chromaticity of the analysed picture. For this purpose, the three input terminals 1, 2 and 3 are respectively connected to the three first inputs of a correcting circuit 5, whose second, third and fourth inputs are respectively connected to the first output of the control circuit 6, to the output of the determination circuit and to the second output of the control circuit 6. In the present embodiment, correcting circuit 5 comprises a subtraction circuit 7 having three first inputs constituting the three first inputs of correcting circuit 5 and three analog multipliers having three first inputs respectiv-ely connected to three outputs of the subtraction circuit 7, having three interconnected second inputs for forming the second input of correcting circuit 5 and having three outputs respectively connected to the three inputs of an adder 9~ The subtraction circuit 7 has a second input constituting the third input of the correcting circuit. The adder 9 has a second input constituting the fourth input of the correcting circuit 5 and three inputs respectively constituting three outputs of correcting cîrcuit 5, which are connected to the three output terminals 15,-16, 17 of the device according to the invention. The second and fourth inputs of correcting circuit 5 respectively receive a value Give) = (Vex supplied by the output Ve of divider 10 and the value F(Ve) supplied by the output of quadripole 11. Subtraction circuit 7 has three outputs respectively supplying three colour difference signals DVel, DVe2 and DVe3. These three signals are processed from signals V 1' V 2' Ve3 and Ve in accordance with the following formulas:
DV = V - V
el el e DVe2 = Ve2 Ve DVe3 = Ve3 Ve Multipliers 21, 22, 23 respectively process three signals DVsl, DVs2 and DVs3 rom signals G(Ve), DV 1' DV 2 and DV 3 in accordance with the following formulas:
DVSl = Dvel G(Ve) DVS2 = DVe2 G(Ve) DVS3 = DVe3 G(Ve) The three outputs of adder 9 respectively supply three signals Vsl, Vs2 and Vs3 processed from signals DVsl, DVs2, DVs3 and F(Ve) in accordance with the following formulas:
VSl = DVsl F(Ve) VS2 = DVs2 + F(Ve) VS3 = DVs3 F(Ve) In accordance with the principle described hereinbefore, correcting circuit 5 transforms the colour informations Vel, Ve2 and Ve3 associated with the overall luminance signal Ve into corrected colour signals Vsl3 Vs2 and VS3 associated with the , corrected overall luminance signal F(Ve). Thus, only the overall luminance has been corrected. The original chromaticity of the analysed picture is not affected by the correction made by correcting circuiL 5.
The invention is not limited to the described and represented embodiment and numerous variants are possible thereto. In particular, ~uadripole 11 can have a random number of variable parameters in order to better adapt the transfer function to the cumulative distribution function. The same applies with regards to the number of samples and the number of amplitude levels of the luminance signal.
Reference has been made in exemplified manner to equalizing the histogram, bu-t any other distribution could be envisagedg whereby this would lead to the calculation of a transfer function differing from the cumulative distribution function.
It should be noted that the control circuit or one of its elements can easily be constructed by means of a microprocessor.
It should also be noted that the overall operation performed on the signals Vel, Ve2 and Ve3 by correcting circuit 5 consists of multiplying each of the three signals by signal G(Ve). Thusg it is easy to prove that:
Vsl = G(Ve) Vel Vs2 = G(Ve) Ve2 VS3 = G(Ve) Ve3 It is therefore possible to construct correcting circuit 5 in a manner different from that described _g_ ~19~
hereinbefore by eliminating the subtraction circuit 7 and adder 9. The embodiment described hereinbefore and shown in Fig 1 is more complex, but it makes it possible to easily obtain the pass band width required for the luminance signal.
It is also possible to directly generate the signal G(Ye) by means of a digital memory. The analog signal of value Ve is then converted into digital values, which are applied to the address inputs of a memory in which a microprocessor has previously stored the values of G(Ve). The output of the memory is then connected to the input of a digital - analog converter, which supplies the signal G(Ve).
In the described embodiment, the matrixing circuit 4 processes a signal Ve corresponding to the overall luminance signal calculated with the standard coefficients (0.11; 0~59; 0.3). However, the invention is also applicable on the basis of a signal Ve corres-ponding to a diffe-rent combination of the colour informations. For example, excellent results have been obtained by taking as signal Ve the signal corresponding to max. (Vel; Ve2; Ve3) should be noted that the invention can easily be applied on the basis of three colour signals of value Eye OR and DB transmitted in colour television. Thus, the treatment which is to be undergone by these three signals can be easily deduced prom that described for the three primary signals EB, En and ER, these two triplets of signals being linked by linear relationships.
Fig 2 shows a second embodiment of the device according to the invention. In this embodiment, the determination circuit supplies a signal of value VeJ
which is not equal to the overall luminance value9 but which ls equal to the highest of the values among the three colour signals ER, EV and EB at the considered sampling time:
Ve = Max (ER, Ev, EB)-Furthermore, the correction consists of correcting the overall luminance, whilst retaining the original chromaticity of the picture when the value G(Ve) is high, but not when it is low. In the first case9 the corrected luminance value is above the original value and the device does not modify the colour saturation. In the second case, the corrected luminance value is below the original value and the perception of the picture is improved by increasing the colour saturation, whilst retaining the said shade.
The signals of values Vel, Ve2 and Ve3 are constituted by the overall luminance signal of value Ey and the colour difference signals of values DR and DBO The control circuit 6 processes the value G(Ve) using a digital process evolved by a microprocessor.
In this embodiment, a determination circuit 4 is constituted by a dematrixing circuit 25 having three inputs constituting the three inputs of the determinat-ion circuit 4 and three outputs supplying colour signals of values ER, EV and EB to three inputs of a selection circuit 26, which determines which of these values is the highest and dls~atches the latter to an output constituting the output of the determination ~9~
circuit 4. The thus determined value V is applied to an input of control circuit 6.
Control circuit 6 comprises an analog - digital converter 27, whose input forms the input of control circuit 6 and which converts the value V from analog into digital form. Control circuit 6 comprises a digital - analog converter 28, whose output forms an output of the control circuit and supplies a signal of value G(Ve)in analog form. Control circuit 6 also has histogram acquisition means 42, a dig;tal integrator 31, a microprocessor 30 and a random access memory 29. Means 32 calculate for each field of a picture, the histogram of 4000 values Ve supplied by the output of the analog - digital converter 27 and supply the values of said histogram to digital integrator 31, which calculates the values of the cumulative distribution function of said histogram and supplies them to an input of microprocessor 30.
Microprocessor 30 has two outputs respectively connected to a writing address input and to a data input of memory 29. It calculates a table of the values of function G(Ve) and stores this table in memory 290 This calculation is performed in two stages, namely the first stage consisting in determining a function F such that the histogram of the values of the corrected signal F(Ve) has a predetermined distribution over its entire scale of values. For example, to have aregular distribution, it is merely necessary for function F(Ve) to be equal to the cumulative distrib-ution function of values Ve. In a second stage, micropro-F(V ) ces~or 30 calculates the values of function G(Ve) = ve whilst taking account of a limitation of the value e G(Ve) to in the present embodiment, in order to never subject the picture to a colour defect and in order not to amplify the noise to the extent of making it visible. In this embodiment, microprocessor 30 calculates 64 values of G(Ve), each of these values being chosen from among 256 possible values coded on 8 bits. These values are stored in memory 29, which has 256Octets. This memory has a reading address input connected to the output of the analog - digital converter 27 and a data output connected to the input of the digital - analog converter 28. For each point of a picture, the output of the determination circuit 4 supplies a value Ve, which is transmitted in digital form to the reading address input of memory 2g. The latter supplies at its data output a digital value G(Ve), which is converted into analog form by digital -analog converter 28 and which is applied to the output of control circuit 6.
Correcting circuit 5 has three analog multipliers 21, 22, 23 having three first inputs and three outputs - respectively constituting three first inputs and three outputs of correcting circuit 5,and having three second inputs. The second input of multiplier 21 is connected to a second input of correcting circui-t 5 and the second inputs of multipliers 22 and 23 are together connected to the output of a weighting circuit 24 - having an input connected to a second input of correct-ing circuit 5.
6~
The weighting circuit 24 is an analog circuit supplying at its output a signal of value H(Ve~ equal to l when G(Ve) is equal to or below l, and a signal of value H(Ye) equal to G(Ve), when the latter is higher than l. The value G(Ve) is transmitted without modification when it is high, so that the chromaticity is retained when the corection consists in increasing the luminance of a shade, whilst the saturation of colour is increased when the luminance of a shade is decreased.
It falls within the scope of the Expert to produce a differently operating weighting circuit 24 and,in particular,it is possible to use a weighting circuit supplying a value such that:
H(Ve) = 1/2.G(Ve) l/2.
In this case, the colour saturation is lncreased when the overall luminance is decreased and the colour saturation is decreased when the overall luminance is increased.
It falls within the scope of the Expert to differently construct the determination circuit 4 an to take for value Ve a different combination ox the colour signals. On taking Ve = Max(ER, Ev, EB) makes it possible to prevent an exaggerated correction of the luminance signal, when one of the values of the colour signals is much higher than the two others.
The present invention relates to devîces or correcting colour inforrnation supplied by a camera of a video transmission system with a view to obtaining, on reception, a picture containing the maximum of visible information.
In black and white picture transmission systems-, a correction device for improving the per eption of ( pictures is already known (u.5. Patent Jo. k 337 514 granted to Applicant on June 29, 19~2.) The process performed by this device consists of correcting the luminance signal supplied by the camera or pickup tube of a black and white camera by means of a non-linear quadripole with variable characteristics and controlled L5 in such a wry that the histogram of the values of the corrected luminance signal his a flat form whatever the shooting conditions, which corresponds to a regular 1 distribution of the values on the scale of said values.
- In its present form, this correction device does not make it possible to improve colour pictures, it only being usable in connection with the irnprovement of the black and white pictures.
BRIEF SUMMARY OF THE INVENTION
The present invention relates to a correction device, which makes it possible to improve the perception of colour pictures. The problem consists in correcting the overall luminance in accordance with the method used ' '' 3~''' by the known device, whilst retaining the origi.nal chromaticity of the analysed picture.
The present invention specifically relates to a device for correcting colour information signals of values V l Ve2 and Ve3 supplied by a television camera, comprising a determination circuit having three inputs respectively receiving the three colour informationsignals and an output, for supplying a signal of value V which is`
a function of the values of the colour information signals ;a control circuit having an input coupled to the output of the determination circuit and having an output for F(Ve) supplying a signal of value G(Ve) = V --- , in which F is a function such that the histogram of values F(Ve) us a function of the values Ve has,a predetermined distribution chosen for improving the perception of images ; and a correction circuit having three first inputs respectively receiving the three colour information signals, a second input coupled to the output of the control circuit and having three outputs constituting the outputs of the device according to the invention,'for supplying three signals which are functions of the value G(Ve) and of the values Vel, Ve2, Ve3 respectively-BRIEF DESCRIPTION OF THE DRAWINGS
The invention is described in greater detail hereinafter relative to non-limitative embodiments and the attached drawings, wherein show:
Fig 1 a first embodiment of the device according to the invention.
'Fig 2 a second embodiment ox the device according to the invention.
. . .
Y
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the first embodiment, the device according to the invention receives three colour information signals of valuec V l V 2 and Ve3 , respectively constituted by three blue green and red signals of values EB, EV and ER respectively applied to the three inputs terminals 1, 2 and 3. At the output terminals 15, 16 and 17 it supplies three corrected colour informa-tion signals of values Vsl, Vs2 and Vs3~ The overall luminance value is.
Ey = 0.11~EB 0.59~EV 0.3DER
= O.ll.V 1 0.59.Ve2 .3Ve3 The correction of the overall luminance consists multiplying this value by a variable coefficient G:
Ey corrected = Ey . G
As the value Ey is a linear combination of Ev, ER
and EB for retaining the chromaticity it is merely necessary to multiply the three values Ev, ER and EB by the same coefficient G. Coefficient G varies when Ey varies, because it is determined in such a way as to flatten the histogram of values Ve of a signal constituted, in this embodiment9 by the overall luminance signal. The correction device according to the invention supplies in this case three colour signals having as the corrected value:
Vsl = G(Ve)~Vel with V = En Vs2 = G(Ve)'Ve2 Vel B
VS3 = G(Ve)~Ve3 V = E
V 3 = ER
Fig 1 is a block diagram of the first embodiment ox the device according to the invention utilizing this --3~
, .
go process. Fig 1 shows the three input terminals 1, 2 and 3 for respectively receiving the three colour signals Vel, Ve2 and Ve3 supplied by the pickup tubes of a colour camera. These three inputs are respectively coupled to the three inputs of a circuit 4 for the determination of a signal Ve, constituted by a matrixing circuit 4. The output of matrixing circuit 4 supplies signal Ve which, in this embodiment9 comprises the overall luminance signal. This signal is deduced from the colour signals Vel, Ve2 and Ve3 in accordance with the following formula:
V 0 11 V + o.59jVe2 3'Ve3~(Vel' e2 e3 corresponding respectively to the blue, green and red colour signals).
The output of matrixing circuit 4 is connected to one input of a control circuit 6. Control circuit 6 comprises the acquisition means 14 of a histogram, an analog quadripole 11 and an analog divider 13, each having an input connected to the input of control eireuit 6 , whilst it also eomprises ealeulation means 13 and auxiliary calculation means 12. Quadripole 11 is non-linear and has variable characteristics regulatable by e-ight control inputs el to e for receiving eight signals defining the transfer parameters of the quadripole. Quadripole 11 is of the known type having a broken line transfer function constituted by a predetermined number of linear segments. In the present embodiment, quadripole 11 has been chosen with eight variable transfer parameters and specifically four pairs, constituted by ~976~
a threshold value and a gain value defining four segments. Such a quadripole comprises four, not shown amplifiers having a regula-table t`hreshold below which each signal is not transmitted and above which the signals are transmitted with a fixed gain. Thus, quadripole 11 supplies a corrected luminance signal F(V ), F being the transfer function of the quadripole.
This signal F(Ve), corresponds to the sum of the four output signals of the four amplifiers of the quadripole and is supplied to a second input of the divider 10 and to a second output of control circuit 6.
Means 14 statis-tically analyse the amplitude distribution of 4000 samples of luminance signals Ve in accordance with 64 given amplitude levels. The 4000 samples result from the analysis of 4000 ranges all covering a frame, and the 64 amplitude levels are distributed at regular intervals over the entire scale of the amplitudes of the luminance. Thus, means 14 make it possible to acquire the function representative of the histogram of the luminance (number of samples for each of the envisaged 64 levels).
The calculation means 13, whose input is connected to the output of means 14, calculated the integral of this function which, by definition, is the cumulative distribution function of the amplitude levels of the samples.
On the basis of this cumulative distribution function, the auxiliary calculating means 12, having an input connected to the output of means 13 and 8 outputs respectively connected to the 8 control inputs el to e8 of the quadripole 11, calculate the values of the 8 transfer parameters Al to A4 and Gl to G4 to be applied to the control inputs el to e$, Ai and Gi (i varying from 1 to 4) respectively representing 5 the threshold values and the gain values of the amplifiers of the quadripo~e, The calculated values are such that the transfer function F realised by quadripole 11 is an approximation by segments of the cumulative distribution function calculated by means 13.
10 The values of the thus determined parameters remain fixed throughout the duration of the following frame.
f Such a transfer function transforms the luminance signal Ve into a corrected signal F(Ve) for which the distribution of the values permits a better 15 vision9 no matter what the shooting conditions.(ln the present embodiment 7 the distribution corresponds to an equalization of the luminance histogram associated with the signal F(V ) ).
The assembly constituted by quadripole 11, the 20 histogram acquisition means 14, the calculating means 13 and the auxiliary calculating means 12 exactly corresponds to the automatic control device described in detail in the aforementioned U.S.Patent no. 4337514 The control circuit 6 also comprises the analog divider 25 10 having two inputs respectively receiving the signals of value Ve and F(Ve) and having an output, constituting the first output of the control circuit, and supplying a signal of value G(Ve) = (Ve) ~t~6~38 The object of the invention is to correct the colour information Vel, Ve2 and Ve3 in order that the overall luminance information, associated with the corrected colour informations, corresponds to the luminance inormation contained in signal F(Ve), whilst retaining the original chromaticity of the analysed picture. For this purpose, the three input terminals 1, 2 and 3 are respectively connected to the three first inputs of a correcting circuit 5, whose second, third and fourth inputs are respectively connected to the first output of the control circuit 6, to the output of the determination circuit and to the second output of the control circuit 6. In the present embodiment, correcting circuit 5 comprises a subtraction circuit 7 having three first inputs constituting the three first inputs of correcting circuit 5 and three analog multipliers having three first inputs respectiv-ely connected to three outputs of the subtraction circuit 7, having three interconnected second inputs for forming the second input of correcting circuit 5 and having three outputs respectively connected to the three inputs of an adder 9~ The subtraction circuit 7 has a second input constituting the third input of the correcting circuit. The adder 9 has a second input constituting the fourth input of the correcting circuit 5 and three inputs respectively constituting three outputs of correcting cîrcuit 5, which are connected to the three output terminals 15,-16, 17 of the device according to the invention. The second and fourth inputs of correcting circuit 5 respectively receive a value Give) = (Vex supplied by the output Ve of divider 10 and the value F(Ve) supplied by the output of quadripole 11. Subtraction circuit 7 has three outputs respectively supplying three colour difference signals DVel, DVe2 and DVe3. These three signals are processed from signals V 1' V 2' Ve3 and Ve in accordance with the following formulas:
DV = V - V
el el e DVe2 = Ve2 Ve DVe3 = Ve3 Ve Multipliers 21, 22, 23 respectively process three signals DVsl, DVs2 and DVs3 rom signals G(Ve), DV 1' DV 2 and DV 3 in accordance with the following formulas:
DVSl = Dvel G(Ve) DVS2 = DVe2 G(Ve) DVS3 = DVe3 G(Ve) The three outputs of adder 9 respectively supply three signals Vsl, Vs2 and Vs3 processed from signals DVsl, DVs2, DVs3 and F(Ve) in accordance with the following formulas:
VSl = DVsl F(Ve) VS2 = DVs2 + F(Ve) VS3 = DVs3 F(Ve) In accordance with the principle described hereinbefore, correcting circuit 5 transforms the colour informations Vel, Ve2 and Ve3 associated with the overall luminance signal Ve into corrected colour signals Vsl3 Vs2 and VS3 associated with the , corrected overall luminance signal F(Ve). Thus, only the overall luminance has been corrected. The original chromaticity of the analysed picture is not affected by the correction made by correcting circuiL 5.
The invention is not limited to the described and represented embodiment and numerous variants are possible thereto. In particular, ~uadripole 11 can have a random number of variable parameters in order to better adapt the transfer function to the cumulative distribution function. The same applies with regards to the number of samples and the number of amplitude levels of the luminance signal.
Reference has been made in exemplified manner to equalizing the histogram, bu-t any other distribution could be envisagedg whereby this would lead to the calculation of a transfer function differing from the cumulative distribution function.
It should be noted that the control circuit or one of its elements can easily be constructed by means of a microprocessor.
It should also be noted that the overall operation performed on the signals Vel, Ve2 and Ve3 by correcting circuit 5 consists of multiplying each of the three signals by signal G(Ve). Thusg it is easy to prove that:
Vsl = G(Ve) Vel Vs2 = G(Ve) Ve2 VS3 = G(Ve) Ve3 It is therefore possible to construct correcting circuit 5 in a manner different from that described _g_ ~19~
hereinbefore by eliminating the subtraction circuit 7 and adder 9. The embodiment described hereinbefore and shown in Fig 1 is more complex, but it makes it possible to easily obtain the pass band width required for the luminance signal.
It is also possible to directly generate the signal G(Ye) by means of a digital memory. The analog signal of value Ve is then converted into digital values, which are applied to the address inputs of a memory in which a microprocessor has previously stored the values of G(Ve). The output of the memory is then connected to the input of a digital - analog converter, which supplies the signal G(Ve).
In the described embodiment, the matrixing circuit 4 processes a signal Ve corresponding to the overall luminance signal calculated with the standard coefficients (0.11; 0~59; 0.3). However, the invention is also applicable on the basis of a signal Ve corres-ponding to a diffe-rent combination of the colour informations. For example, excellent results have been obtained by taking as signal Ve the signal corresponding to max. (Vel; Ve2; Ve3) should be noted that the invention can easily be applied on the basis of three colour signals of value Eye OR and DB transmitted in colour television. Thus, the treatment which is to be undergone by these three signals can be easily deduced prom that described for the three primary signals EB, En and ER, these two triplets of signals being linked by linear relationships.
Fig 2 shows a second embodiment of the device according to the invention. In this embodiment, the determination circuit supplies a signal of value VeJ
which is not equal to the overall luminance value9 but which ls equal to the highest of the values among the three colour signals ER, EV and EB at the considered sampling time:
Ve = Max (ER, Ev, EB)-Furthermore, the correction consists of correcting the overall luminance, whilst retaining the original chromaticity of the picture when the value G(Ve) is high, but not when it is low. In the first case9 the corrected luminance value is above the original value and the device does not modify the colour saturation. In the second case, the corrected luminance value is below the original value and the perception of the picture is improved by increasing the colour saturation, whilst retaining the said shade.
The signals of values Vel, Ve2 and Ve3 are constituted by the overall luminance signal of value Ey and the colour difference signals of values DR and DBO The control circuit 6 processes the value G(Ve) using a digital process evolved by a microprocessor.
In this embodiment, a determination circuit 4 is constituted by a dematrixing circuit 25 having three inputs constituting the three inputs of the determinat-ion circuit 4 and three outputs supplying colour signals of values ER, EV and EB to three inputs of a selection circuit 26, which determines which of these values is the highest and dls~atches the latter to an output constituting the output of the determination ~9~
circuit 4. The thus determined value V is applied to an input of control circuit 6.
Control circuit 6 comprises an analog - digital converter 27, whose input forms the input of control circuit 6 and which converts the value V from analog into digital form. Control circuit 6 comprises a digital - analog converter 28, whose output forms an output of the control circuit and supplies a signal of value G(Ve)in analog form. Control circuit 6 also has histogram acquisition means 42, a dig;tal integrator 31, a microprocessor 30 and a random access memory 29. Means 32 calculate for each field of a picture, the histogram of 4000 values Ve supplied by the output of the analog - digital converter 27 and supply the values of said histogram to digital integrator 31, which calculates the values of the cumulative distribution function of said histogram and supplies them to an input of microprocessor 30.
Microprocessor 30 has two outputs respectively connected to a writing address input and to a data input of memory 29. It calculates a table of the values of function G(Ve) and stores this table in memory 290 This calculation is performed in two stages, namely the first stage consisting in determining a function F such that the histogram of the values of the corrected signal F(Ve) has a predetermined distribution over its entire scale of values. For example, to have aregular distribution, it is merely necessary for function F(Ve) to be equal to the cumulative distrib-ution function of values Ve. In a second stage, micropro-F(V ) ces~or 30 calculates the values of function G(Ve) = ve whilst taking account of a limitation of the value e G(Ve) to in the present embodiment, in order to never subject the picture to a colour defect and in order not to amplify the noise to the extent of making it visible. In this embodiment, microprocessor 30 calculates 64 values of G(Ve), each of these values being chosen from among 256 possible values coded on 8 bits. These values are stored in memory 29, which has 256Octets. This memory has a reading address input connected to the output of the analog - digital converter 27 and a data output connected to the input of the digital - analog converter 28. For each point of a picture, the output of the determination circuit 4 supplies a value Ve, which is transmitted in digital form to the reading address input of memory 2g. The latter supplies at its data output a digital value G(Ve), which is converted into analog form by digital -analog converter 28 and which is applied to the output of control circuit 6.
Correcting circuit 5 has three analog multipliers 21, 22, 23 having three first inputs and three outputs - respectively constituting three first inputs and three outputs of correcting circuit 5,and having three second inputs. The second input of multiplier 21 is connected to a second input of correcting circui-t 5 and the second inputs of multipliers 22 and 23 are together connected to the output of a weighting circuit 24 - having an input connected to a second input of correct-ing circuit 5.
6~
The weighting circuit 24 is an analog circuit supplying at its output a signal of value H(Ve~ equal to l when G(Ve) is equal to or below l, and a signal of value H(Ye) equal to G(Ve), when the latter is higher than l. The value G(Ve) is transmitted without modification when it is high, so that the chromaticity is retained when the corection consists in increasing the luminance of a shade, whilst the saturation of colour is increased when the luminance of a shade is decreased.
It falls within the scope of the Expert to produce a differently operating weighting circuit 24 and,in particular,it is possible to use a weighting circuit supplying a value such that:
H(Ve) = 1/2.G(Ve) l/2.
In this case, the colour saturation is lncreased when the overall luminance is decreased and the colour saturation is decreased when the overall luminance is increased.
It falls within the scope of the Expert to differently construct the determination circuit 4 an to take for value Ve a different combination ox the colour signals. On taking Ve = Max(ER, Ev, EB) makes it possible to prevent an exaggerated correction of the luminance signal, when one of the values of the colour signals is much higher than the two others.
Claims (8)
1. A device for correcting colour information signals of values Ve1, Ve2 and Ve3 supplied by a television camera.
comprising a determination circuit having three inputs respectively receiving the three colour information signals and an output, for supplying a signal of value Ve which is a function of the values of the colour information signals; a control circuit having an input coupled to the output of the determination circuit and having an output for supplying a signal of value G(Ve) = , in which F
is a function such that the histrogram of values F(Ve) as a function of the values Ve has a predetermined distribution chosen for improving the perception of images ; and a correction circuit having three first inputs respectively receiving the three colour informations signals, a second input coupled to the output of the control circuit and having three outputs constituting the outputs of the device according to the invention, for supplying three signals which are functions of the value G(Ve) and of the values Ve1, Ve2, Ve3 respectively.
comprising a determination circuit having three inputs respectively receiving the three colour information signals and an output, for supplying a signal of value Ve which is a function of the values of the colour information signals; a control circuit having an input coupled to the output of the determination circuit and having an output for supplying a signal of value G(Ve) = , in which F
is a function such that the histrogram of values F(Ve) as a function of the values Ve has a predetermined distribution chosen for improving the perception of images ; and a correction circuit having three first inputs respectively receiving the three colour informations signals, a second input coupled to the output of the control circuit and having three outputs constituting the outputs of the device according to the invention, for supplying three signals which are functions of the value G(Ve) and of the values Ve1, Ve2, Ve3 respectively.
2. A device according to claim 1 in which the correction device comprises a first, a second, and a thrid multiplier, each having a first and a second input, as well as an output, their first inputs being respectively coupled to the three first inputs of the correcting circuit, their second inputs being coupled to the second input of the correcting circuit, and their third outputs being respec-tively coupled to the three outputs of the correcting circuit.
3. A device according to claim 2 in which the colour in-formation signals are the red, green and blue colour signals, and in which the second inputs of the multipliers are connected to the second input of the correcting circuit.
4. A correcting device according to claim 3 in which the control circuit also comprises a second output supplying a signal of value F(Ve) and in which the correcting circuit also comprises a third input connected to the output of the determination circuit, a fourth input connected to the second output of the control circuit; a subtraction circuit having three first inputs respectively connected to the three first inputs of the correcting circuit, a second input connected to the third input of the correcting circuit and three outputs respectively connected to the three first inputs of the multipliers for respectively supplying values Ve1-Ve, Ve2-Ve, Ve3-Ve ;an addition circuit having three first inputs respectively connected to the three outputs of the multipliers, a second input connected to the fourth input of the correcting circuit and three outputs respectively connected to the three outputs of the correcting circuit for respectively supplying the values D VS1+F(Ve), D VS2+F(Ve), D VS2+F(Ve), in which D VS1, D VS2 , D VS3 are values respectively supplied by the outputs of the three multipliers.
5. A device according to claim 2 in which the colour in-formation signals are constituted by the overall luminance signal and two colour difference signals and are respectively applied to the first inputs of the three multipliers, where the correcting circuit also comprises a weighting circuit having an input connected to the second input of the correcting circuit and having an output, where the second input of the first multiplier is connected to the second input of the correcting circuit, and wherein the second inputs of the second and third multipliers are connected to the output of the weighting circuit, the weighting circuit multiplying the value G(Ve) by a coefficient which varies as a function of the value G(Ve).
6. A device according to claim 1 in which the control device comprises a non-linear quadripole with variable characteristics, having a control input making it possible to regulate its transfer function, an input connected to the input of the control circuit and having an output for supplying the signal of value F(Ve), a divider having a first input connected to the input of the control device, a second input connected to the output of the quadripole and an output connected to the first output of the control device for supplying the signal of value G(Ve) = and means for determining the histogram of values Ve and then the cumulative distribution function of these values and for deducing therefrom values of parameters defining the function F and such that the histogram of the values F(Ve) as a function of the values Ve has a predetermined distribution, with an input connected to the input of the control circuit and having an output connected to the control input of the quadripole.
7. A device according to claim 1 in which the control circuit comprises means for determining the histogram of values Ve and then the cumulative distribution function of these values and for deducing therefrom the values of the function F(Ve), such that its histogram as a function of the values Ve has a predetermined distribution, having an input coupled to the input of the control circuit and an output, a microprocessor having an input connected to the output of these means, having a data output and an address output for calculating the values of ?
and a random access memory for storing the values of , having a writing address input connected to the address output of the microprocessor, a data input connected to the data output of the microprocessor and a reading address input coupled to the input of the control circuit and having a data output coupled to the output of the control circuit.
and a random access memory for storing the values of , having a writing address input connected to the address output of the microprocessor, a data input connected to the data output of the microprocessor and a reading address input coupled to the input of the control circuit and having a data output coupled to the output of the control circuit.
8. A device according to claim l in which the signal of value Ve is constituted by the colour information signal having the highest value at the considered sampling time.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR8110253A FR2506549A1 (en) | 1981-05-22 | 1981-05-22 | DEVICE FOR CORRECTING COLOR INFORMATION PROVIDED BY ANALYZER TUBES OF A CAMERA WITH A VIEW TO IMPROVING IMAGE PERCEPTION |
| FR8110253 | 1981-05-22 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1197608A true CA1197608A (en) | 1985-12-03 |
Family
ID=9258804
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000403228A Expired CA1197608A (en) | 1981-05-22 | 1982-05-18 | Device for correcting colour information supplied by a television camera with a view to improving the perception of pictures |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4499486A (en) |
| EP (1) | EP0067083B1 (en) |
| JP (1) | JPS57197988A (en) |
| CA (1) | CA1197608A (en) |
| DE (1) | DE3260247D1 (en) |
| FR (1) | FR2506549A1 (en) |
Families Citing this family (20)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4638352A (en) * | 1983-09-16 | 1987-01-20 | Hitachi, Ltd. | Color video camera signal processing circuit |
| JPS60151786A (en) * | 1984-01-19 | 1985-08-09 | Fuji Photo Film Co Ltd | Processing method and device of radiation picture information reading gradation |
| FR2575884B1 (en) * | 1985-01-08 | 1988-07-08 | Thomson Video Equip | DEVICE FOR REDUCING THE DYNAMICS OF THREE COLOR SIGNALS REPRESENTING AN IMAGE |
| US4764971A (en) * | 1985-11-25 | 1988-08-16 | Eastman Kodak Company | Image processing method including image segmentation |
| JPS6354144A (en) * | 1986-08-25 | 1988-03-08 | 株式会社東芝 | Electronic endoscope apparatus |
| JPH0669438B2 (en) * | 1987-04-24 | 1994-09-07 | 株式会社東芝 | Endoscope device |
| DE3629403C2 (en) * | 1986-08-29 | 1994-09-29 | Agfa Gevaert Ag | Method of correcting color saturation in electronic image processing |
| DE3629396C2 (en) * | 1986-08-29 | 1993-12-23 | Agfa Gevaert Ag | Electronic image processing method |
| JP2522296B2 (en) * | 1987-03-31 | 1996-08-07 | ソニー株式会社 | Video signal gradation control circuit |
| US4868651A (en) * | 1988-05-17 | 1989-09-19 | S&S Inficon, Inc. | Digital radiography with image brightness and contrast normalization |
| JP2582140B2 (en) * | 1988-10-31 | 1997-02-19 | 株式会社日立製作所 | Projection display |
| CA2040672C (en) * | 1990-04-26 | 1995-05-30 | Masaaki Kanashiki | Image signal processing apparatus |
| US5137364A (en) * | 1991-01-31 | 1992-08-11 | Mccarthy Cornelius J | Optical spectral analysis apparatus |
| BE1007590A3 (en) * | 1993-10-01 | 1995-08-16 | Philips Electronics Nv | Video signal processing circuit. |
| JP3134660B2 (en) * | 1994-04-14 | 2001-02-13 | 松下電器産業株式会社 | Color conversion method and color conversion device |
| JP3408316B2 (en) * | 1994-04-18 | 2003-05-19 | 日本フィリップス株式会社 | Knee circuit |
| JP3852956B2 (en) * | 1997-03-06 | 2006-12-06 | 松下電器産業株式会社 | Gamma correction device |
| EP1070423A1 (en) * | 1999-02-05 | 2001-01-24 | Koninklijke Philips Electronics N.V. | Histogram equalization |
| EP1404116A1 (en) * | 2002-09-25 | 2004-03-31 | Dialog Semiconductor GmbH | Method for fast color saturation control |
| JP2008242733A (en) * | 2007-03-27 | 2008-10-09 | Seiko Epson Corp | Image processing apparatus |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2018149C3 (en) * | 1970-04-16 | 1975-08-28 | Robert Bosch Gmbh, 7000 Stuttgart | Process for increasing the sharpness of color television pictures and circuit arrangement for carrying out the process |
| US3684825A (en) * | 1971-02-19 | 1972-08-15 | Rca Corp | Contrast compression circuits |
| US3979555A (en) * | 1975-05-27 | 1976-09-07 | Hughes Aircraft Company | Histogram equalization system for display improvement |
| US3983320A (en) * | 1975-08-25 | 1976-09-28 | Hughes Aircraft Company | Raster display histogram equalization |
| GB2046051B (en) * | 1979-03-29 | 1983-01-26 | Philips Electronic Associated | Real time histogram modification system for image processing |
| FR2456448A1 (en) * | 1979-05-11 | 1980-12-05 | Thomson Csf | DEVICE FOR AUTOMATICALLY CONTROLLING THE TRANSFER FUNCTION OF A VIDEO FREQUENCY TRANSMISSION SYSTEM WITH A VIEW TO IMPROVING IMAGE PERCEPTION |
| IL58119A (en) * | 1979-08-27 | 1983-03-31 | Yeda Res & Dev | Histogram image enhancement system |
| US4315319A (en) * | 1980-02-01 | 1982-02-09 | Rockwell International Corporation | Non-linear signal processor |
| US4394744A (en) * | 1981-02-12 | 1983-07-19 | The United States Of America As Represented By The Secretary Of The Navy | Real-time amplitude histogram shaper |
-
1981
- 1981-05-22 FR FR8110253A patent/FR2506549A1/en active Granted
-
1982
- 1982-05-04 DE DE8282400821T patent/DE3260247D1/en not_active Expired
- 1982-05-04 EP EP82400821A patent/EP0067083B1/en not_active Expired
- 1982-05-18 CA CA000403228A patent/CA1197608A/en not_active Expired
- 1982-05-19 US US06/379,945 patent/US4499486A/en not_active Expired - Fee Related
- 1982-05-21 JP JP57087176A patent/JPS57197988A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| EP0067083B1 (en) | 1984-06-13 |
| FR2506549B1 (en) | 1983-10-07 |
| EP0067083A1 (en) | 1982-12-15 |
| FR2506549A1 (en) | 1982-11-26 |
| JPS57197988A (en) | 1982-12-04 |
| DE3260247D1 (en) | 1984-07-19 |
| US4499486A (en) | 1985-02-12 |
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